High temperature furnace insulated wall construction



Nov. 19, 1935. A. s'. NICHOLS 2,021,742

HIGH TEMPERATURE FURNACE INSULATED WALL CONSTRUCTION Filed June 18, 1934gil Patented Nov. 19, 1935 UNIT ED STATES PATENT GFFICE HIGH TEMPERATUREFURNACE INSULATED WALL CONSTRUCTION Application June 18, 1934, SerialNo. 731,029

4 Claims.

This invention relates to wall constructions for high temperaturefurnaces and the like involving the use of insulating material, among.other objects aims to provide a durable construction of this charactercapable of resisting the disintegrating forces to whichv a structure ofthis character is subjected.

` The invention may be readily understood by reference to oneillustrative construction embodying the invention and shown in theaccompanying drawing;

In said drawing:

Fig. 1 is a sectional elevation of a portion of a furnace wall; and

Fig. 2 is a plan section of aportion of such wall taken approximately onthe plane 2-2 of Fig. 1.

The construction of insulated walls for high temperature furnaces andthe like involves problems not encountered in ordinary insulatedstructures. In an open hearth furnace, for example, the expansion of therefractory side Wall material (usually silica brick above the chargingfloor) is about three-sixteenths of an inch per foot. The ensuingmovement of the walls has made it difficult to prevent separation of therefractory wall from the insulating wall under the methods heretoforeemployed for supporting the insulating material. Owing to the hightemperatures developed and for other reasons, the insulating materialhas not generally been anchored to the refractory material but issupported by external means independent of the refractory wall.Moreover, the insulating materials heretofore available which arecapable of resisting high temperatures (2000 F. and up) cannotsatisfactorily withstand disintegration by the crushing stressesdeveloped by the expanding refractory walls or are' otherwise notsuitable for conditions present in the construction and' operation ofhigh temperature furnaces.

The present invention enables the construction of an insulated hightemperature furnace wall wherein the insulating material is of acharacter which will resist disintegration under the aforesaidcompressive stresses and is otherwise appropriate for high temperaturefurnace conditions and wherein the insulating wall is safely andpermanently anchored to the refractory wall so as to provide a durableunitary structure.

The illustrative construction comprises a wall l0 of refractory materialherein consisting of a plurality of courses of refractory brick Il whosecharacter and dimensions depend largely upon the type of furnace andoperating temperatures. For walls above the charging floo-r of an openand hearth furnace, silica brick are generally employed to form a wallthickness of about eighteen inches,generally formed by two thicknessesof brick. Variation in refractory wall thickness may be secured bychanging the method of laying the 5: brick. For lower temperaturefurnaces, thinner Walls may be employed and in some cases the typicalclay fire brick may be used. As here shown, the refractory brick walland the insulating wall l2 have been combined in a unitary 10 structureby the use of high fusion point, corrosion resisting metallic ties I3.An appropriate alloy steel for such ties is a chromium alloy steel whichhas a high corrosion resisting or scaling temperature of about 2100 F.and a melting 15` range of 2710 F. to 2750 F., thereby enabling the4ties to resist disintegration by corrosion (i. e. scaling) at the hightemperatures to which they are subjected. An alloy steel of thischaracter is procurable on the open market; it is 20 made for example bythe United States Steel Corporation and identified as U S S 27 stainlessand heat resisting steel. 'I'hese ties are advantageously flat incharacter so as to pass through the joints between the brick withoutincreasing 25 the joint thickness. It will be understood that in hightemperature furnace walls the joint thickness between brick is minimizedbecause of the relative lack of stability of the fire clay mortargenerally employed, and only sufficient mortar is used to level off theinequalities of contiguous contacting brick faces. Of course the tie mayhave mechanical anchoring means such as perforations, notches, tongues,etc., and if the mortar joint be relatively thick, the tie mayadvantageously be distorted transversely of the mortar joint bycorrugations, etc. As here shown, the tie i3 extends to an inner face ofa refractory brick and has an angularly bent portion I4 engaging suchinner face to anchor the tie in place. For refractory walls of doublethickness (usually employed in furnaces developing exceedingly hightemperatures) the tie preferably extends only to the inner face I5 ofthe outer thickness I6 and is protected by the inner thickness ll. Inksingle thickness refractory walls (usually used for the lowertemperature furnaces) the tie may safely extend to the inner face of thewall since it will resist corrosion up to temperatures of 2l00 F.(whereas ordinary iron and steel corrode rapidly at about 1000" F.).Generally the prong of the tie is coated over by deposits from thefurnace and is thereby additionally protected. It is not necessarytherefore to 55- rely upon the strength of the mortar between the bricksto hold the tie in place.

It is desirable that the horizontal brick joints I8 and i9 of therefractory brick and insulation brick frequently align to permit theready application of ties; and therefore the vertical thickness of theinsulation brick and refractory brick should either be the same or theirrelative thicknesses so proportioned that joint alignment willl occurevery few courses. The tie may extend to the outer face of theinsulation brick to be anchored there by another angularly bent portionor if, as in the present instance, the brick may be readily penetratedwithout disintegration, the tie may have a pronged extremity which maybe easily pressed into the brick as at 20. The latter arrangement ispreferable since the construction is not affected by variations intransverse brick thickness.

The number of ties employed in each course as Well as the verticalspacing ties is generally determined by the character of the Wall andthe stresses imposed by expansion under heat.

A penetrable insulation brick of the character above referred to may beformed from granules of exfoliated vermiculite mixed with a smallquantity of plastic clay bound together superficially to provide a firmreinforcing shell for the brick. Exfoliated vermiculite is an alterationproduct of particles of certain micaceous minerals, such as biotite,which exfoliate or expand to many times their original size upon theapplication of heat to produce a granular insulating material bothhighly refractory and extremely light in weight (about six pounds percubic foot). Heat causes the multitude of micaceous laminae of thevermiculite to separate minutely, thus providing a multitude ofsubstantially parallel planes of highly polished surfaces which not onlymake transfer of heat extremely diiiicult, but substantially reflectheat waves. The particles are readily compressible in the direction oftheir expansion, thus rendering the interior of the brick compressibleand making it capable of absorbing without disintegration thecompressive forces which develop in the operation of high temperaturefurnaces and preventing their transmission to retaining structures, aspresently explained. The plastic clay in this case serves somewhat as amatrix to protect the compressible particles of vermiculite but ispreferably not used in such quantities as to substantially increase theweight of the brick or impair its insulating efficiency. The

exfoliated vermiculite is both extremely refractory and a highlyefficient insulator which does not lose its insulating efficiency whensubjected to the high temperatures encountered adjacent the refractorywall of an open hearth furnace.

To facilitate formation of the brick, a liquid binder is used to form aplastic mass which is molded into brick form and thereupon dried. Thedrying action causes the binding material to migrate to the surface ofthe brick to form a hard durable shell on the brick. Even though thebinder be destroyed after the brick is in place and subjected to hightemperature, disintegration does not result since the clay materialthereupon serves as a satisfactory binder. While the surface of thebrick is hard, it can be easily penetrated by a prong of the metallicties I3 since the interior of the brick is quite compressible.

The above described compressible character of the brick makes itparticularly advantageous for use in the typical furnace constructionwherein the insulatingwall is either enclosed by a metallic shell orabuts in places the typical buck-stays 2| used in open hearth and otherfurnace constructions. It will be understood that the buck-stays extendvertically on opposite sides of the furnace and are connected togetherby tie rods extending across the furnace above its roof. Upon expansionof the furnace wall the outer wall of insulating material yields (i. e.compressed) under the forces developed and thereby protects thebuck-stays or other surrounding metal retaining structure fromdisruption and distortion. A hard and incompressible outer layer ofbrick would of course transmit the expansive forces to the outerretaining structure and there- -by distort or seriously damage it. Onthe other hand, bricks or blocks made from friable insulating materialssuch as diatomaceous earth and ceramic bonded materials would be crushedand would disintegrate under the aforesaid compressive stresses and thepowdered insulating material would eventually sift down and expose therefractory wall. This is quite serious particularly where the furnacewall is enclosed in a metallic shell and the absence of insulation isnot immediately visible. The compressible character of the exfoliatedvermiculite in the insulation brick above described enables the brick tobe compressed without disintegration, There is no danger therefore ofdeveloping exposed points in the furnace wall. Upon cooling of thefurnace and contraction of the refractory wall, the metallic tiesprevent the separation of the insulating wall which would otherwiseensue. The wall structure therefore is unitary in character under theexpanding and contracting movel 45 1. A high temperature furnaceconstruction comprising in combination a refractory wall formed of aplurality of courses of refractory brick, an outer wall in contact withsaid refractory wall and formed of a pluralityr of courses ofcompressible insulating brick, a metallic retaining structure bearingagainst the outer face of said outer wall, said insulating brick beingcompressible and adapted to be compressed by the expansion of therefractory brick wall against the metallic retaining structure and to becompressed thereby without disintegration, certain joints between thebrick ineach wall being in alignment, and ties extending between saidjoints and having projections in engagement with the brick in each ofthe walls to tie the walls together, said ties being formed of flatstrips of high temperature corrosion resisting steel to withstand thehigh temperatures in said furnace.

2. A high temperature furnace construction comprising in combination arefractory wall formed of a plurality of courses of refractory brickadapted to expand substantially under heat, a separate outer wall of,brick having different expansion characteristics from said refractorybrick, said outer wall being independent of said refractory brick wallso that each wall may move independently under expansion or contraction,and flexible metallic ties made of high temperature corrosion resistingalloy steel and having angular projections engaging the brick in eachWall thereby to hold the Walls against substantial separation under thedisruptive forces developed in the operation of the furnace.

3. A high temperature furnace construction wherein the high temperaturesinvolve substantial expansion of the furnace structure comprising incombination a refractory lining Wall made of refractory brick, an outerinsulating Wall made of brick having different expansion characteristicsfrom said refractory brick, said Walls being unconnected except byflexible metallic ties made of a high temperature corrosion resistingalloy, said ties having angular projections adapted to engage brick ineach of said Walls to tie the walls together.

4. A high temperature furnace construction wherein the high temperaturesinvolve substantial expansion of the furnace structure comprising incombination a refractory wall formed of a plurality of courses ofrefractory brick, an outer Wall in contact with said refractory wall andformed of a plurality of courses of brick formed of particles ofexfoliated vermiculite, said brick having a penetrable outer shell,certain joints between the brick in each Wall being in alignment, andhigh temperature alloy steel ties extending between said joints to tiethe Walls together, said ties having prongs which penetrate the outershell of said insulating brick.

ARTHUR S. NICHOLS.

